Electrical component formed with dielectric jacket



Feb. 11, 1964 J. R. TUZlNSKl 3,121,192

ELECTRICALCOMPONENT FORMED WITH DIELECTRIC JACKET Filed Oct. 17. 1957 INVENTOR JOHN R. TUZIN5I I BY zwmflm w y ATTORNEYS United States art 3,121,192 ELECTRICAL COMPONENT FORMED WITH DIELECTRIC JACKET John Tuzinski, St. Paul, Minn., assignor to Minnesota Mining Manufacturing Company, St. Paul, Minn, a corporation of Delaware Filed Oct. 17, 1957, Ser. No. 690,799 1 Claim. (Cl. 317158) This invention relates to a new method for providing dielectric jackets or sheaths about desired parts of electrically conductive portions of solid bodies, such as for example, the winding of solenoid coils. The invention also relates to new and improved articles formed by such method.

In the case of providing a dielectric sheath about a solenoid coil by dipping the coil in resin and then curing the resin, a problem arises in that resin clings to the internal dimension or diameter of the coil and changes the same. Where the inside diameter acts as a guide for a sliding armature, such a'coating tends to reduce internal tolerances and to interfere with smooth operation of the armature. This invention obviates such difiiculties in the manufacture and use of solenoid coils and the like.

Another advantage accruing in the practice of this invention lies in the reduced amount of insulating material needed to adequately provide a dielectric sheath about solenoid coils, relay coils, transformers, motor control coils, etc.

By following the teaching of this invention, great sirnplicity is introduced into the art of providing insulating sheaths over various electrically conductive portions of solid bodies. Cumbersome molds and the like for controlling and limiting the portion of a body to be ensheathed are rendered unnecessary by this invention. 7

I will now describe my invention with reference to the accompanying drawing made a part hereof wherein:

FIGURE 1 is a perspective view of a solenoid coil and an extrusion nozzle used to ensheath the windings of the coil with a dielectric resin material; and

FIGURE 2 is a perspective view of a solenoid coil provided with an insulating sheath according to this invention, the ensheathe'd coil having a section cut away so as to illustrate the lack of penetration by the resin insulating material into and between the wires in the Winding of the coil.

Referring now to the drawing, which is illustrative and not limitative of my invention, a solenoid coil 10 is suitably mounted on a rotatable shaft (not shown in the drawing) with its axes parallel with the elongated orifice 11 of an extrusion nozzle 12. As may be noted in FIG- URE l, the elongated orifice 11 of the nozzle 12 extends slightly around the sides 13 of the flattened nozzle. In effect, a small portion of each edge of the flattened nozzle 12 is cut away so as to permit plastic 14 emerging from the orifice 11 to spread outwardly at its edge. The ribbon of plastic is extruded from the orifice by applying suitable pressure (the means for applying pressure being not shown in the drawing) upon the plastic in the extrusion cylinder 15. Extrusion is accomplished directly upon the winding 16 between the end flanges 17 of the solenoid coil 10, and the plastic ribbon rests directly upon the winding 16 of the coil.

As the ribbon of plastic is extruded from the orifice 11, the coil 10 is rotated on its shaft so as to lay an essentially uniform layer of insulating plastic completely about the 18, and thus assure adequate covering of the coil winding thereadjacent. Likewise, after the coil has been rotated on its shaft through almost one complete revolution, extrusion of plastic from the elongated orifice is continued for a moment while maintaining the coil stationary so as to achieve a slight build-up of plastic on the other side of the terminals 18. Valve 19 may be used to start and stop plastic extrusion. By following the aforedesignated procedure, a complete insulating sheath about the winding of the solenoid coil is achieved.

In order to prevent the terminals of the coil from being coated with the ribbon of plastic they may be provided with removable protective clips or the like. Controlled extrusion of the ribbon of plastic also may be employed to prevent coating of such terminals. Also, the angle of the extrusion nozzle with respect to the surface to be coated may be varied during coating.

While I illustrate laying a ribbon of plastic on a coil by maintaining the extrusion orifice stationary and rotating the coil therebeneath, it will be understood that the reverse may be employed. For example, the coil may be maintained stationary and the extrusion nozzle rotated therearound. Also, if desired, both the coil and the extrusion nozzle may be moved or rotated to a certain extent during a ribbon laying cycle.

Little or no penetration of the extruded ribbon of plastic 14 into the wire winding 16 of the coil takes place during the ribbon laying cycle aforediscussed, yet intimate contact between the ribbon of plastic and the external layer of the winding is achieved, as desired, and as illustrated in FIGURE 2. Additionally, the extruded ribbon of plastic flows into contact with the end shoulders to form a seal therewith.

A specific non-limitative example will now be offered so as to further illustrate the unique features and essential principles of the invention.

. Example Part A: Parts by weight Liquid epoxy resin 16.42 Talc 16.67 Pigment (red iron oxide) 0.22 Pigment (carbon black) 0.02

PartB:

Tetrapropenyl succinic anhydride 19.72 Polypropylene glycol dimaleate 13.33 Pigment (carbon black) 0.03 Quinoline 0.26 Dimethyldioctadecyl ammonium bentonite 3.33 Talc 30.00

The epoxy resin employed had a viscosity of about to 200 poises at room temperature, a 1,2-epoxy equivalency greater than one, an oxirane oxygen content of about 8.5%, and a melting point of about 812 C. It is available commercially from the Shell Development Corporation as Epon 828 and is formed by the reaction between epichlorhydrin and Bisphenol A. The preparation of epoxy resins, or other suitable resins to employ as herein taught, forms no part of this invention. Many different resins are suitable to employ according to the teachings herein, as will be readily understood by those skilled in the art.

The ingredients of part A above were stirred together and passed through a paint mill to form a smooth dispersion.

Carbon black and tetrapropenyl succinic anhydride of the part-B ingredients were milled together on a paint mill until well dispersed and then added to the remaining ingredients listed in part B. The part B mixture was then given two passes through a tightly-set, high-speed three roller paint mill. Two parts of the part B mixture and one part of the part A mixture were then blended together and placed in an extrusion cylinder.

In the extrusion cylinder, the plastic was maintained at about 140 F. and was forced from the cylinder through the extrusion orifice into a ribbon by air pressure. Simultaneously with the emerging of the ribbon from the extrusion orifice, it was laid in contact with the winding of the solenoid coil, as aforediscussed. For this operation I sometimes pre-heat the solenoid coil to be ensheathed to about 250 F., but suitable results are obtained by leaving the coil at room temperature for the ensheathing operation.

The Width of the extrusion orifices was slightly less than the inside spacing between the end flanges of the coil. The plastic resinous mix was thixotropic and as it emerged from the extrusion orifice, it slowly flowed into contact with the coil winding and end flanges, but did not sag and drip from the coil. During extrusion of the plastic mass, the coil was rotated at a rate approximately the same as the emersion of plastic from the orifice so as to thereby facilitate laying of a uniformly thick sheath of insulating material about the coil winding. However, for an instant immediately after starting extrusion of the plastic mass, and immediately before terminating extrusion, the coil was actually held stationary so as to achieve a slight buildup of insulation at the base near the electrical terminals thereof.

After applying the ribbon of plastic as aforenoted, the ribbon ensheathed coil was transferred to a curing oven where it was heated to about 250 F. for about two hours to eifect curing of the epoxy resin sheath. No problem with respect to oven dripp ugs was encountered.

If desired, the electrical terminals of the solenoid coil may be covered with polytetrafiuoroethylene to prevent resin from encapsulating them in the foregoing operation. Advantageously, the epoxy resin mixture employed in this example does not adhere well to polytetrafluoroethylene, and removal of the polytetrafluoroethylene coverings from the terminals can easily be accomplished after curing. Instead of employing a cover over the terminals, one may press the terminals through a sheet of polytetrafiuoroethylene or the like prior to curing the resin plastic ribbon. By so doing, the plastic near or adjacent the terminals can be flattened, thus obviating any possible tear-drop formation of plastic in this area which might interfere with use of the solenoid at a later date.

A wide variety of dielectric resinous masses may be employed as the material to be extruded according to the teachings herein. For example, thixotropic polyesters, butyl rubbers, polyamide resins, phenolic resins, alkyds, as well as other thermoplastic and thermosetting resinous plastic materials may be employed. In the event a thermoplastic material is chosen, extrusion is suitably accomplished under heat conditions, followed by cooling.

The viscosity of plastic masses used in this process should preferably be adjusted, as by the addition of fillers or other materials or agents, so that under the temperature employed for extrusion, as well as under the temperature employed for any necessary heat-curing, they are not actually liquified and thus not caused to drip from the desired area of an article to be jacketed. The thick ness of insulation needed for ensheathing components as here discussed varies depending upon the electrical component treated, and in this respect thisinvention offers the advantage of achieving desired thickness by varying the orifice for extrusion, rate of extrusion, thixotropy of the plastic, its viscosity, the temperature conditions for extruding the ribbon and for curing, etc

In practice, it is preferable to employ thixotropic, thermosetting, dielectric plastic materials and to extrude them at room temperature, or under somewhat raised temperature conditions. After extruding thermosetting plastics into a ribbon and laying. the ribbon in place as aforediscussed, a short heating step is employed to accomplish thermosetting or curing of the mass. It is to be understood, however, that resins which set-up or cure at room temperature may alsoibe employed in the practice of this invention.

Instead of extruding a ribbon as a flat layer as illustrated in the drawing, it may be extruded as a curved layer, or a layer of other transverse configuration. In this manner limited areas of buss bars, specially-shaped motor windings, and the like may conveniently be provided with dielectric sheaths using a minimum of material, of time and of apparatus.

It will be understood that many variations of the foregoing process may be employed without departing from the essential features and principles of my invention, as further set forth in the claim appended hereto.

I claim:

As a new article of manufacture: an article comprising an electrical winding of wire coated with a unitary seamless fused sheath of thermoset epoxy plastic with essentially no penetration of said plastic between the wire loops of said winding, said sheath being sealed in intimate contact with said winding of wire and being formed by thermosetting a freshly extruded flowable ribbon of said plastic on said winding of wire.

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